Devices, systems and methods for electrostatic force enhanced semiconductor bonding

ABSTRACT

Various embodiments of microelectronic devices and methods of manufacturing are described herein. In one embodiment, a method for enhancing wafer bonding includes positioning a substrate assembly on a unipolar electrostatic chuck in direct contact with an electrode, electrically coupling a conductor to a second substrate positioned on top of the first substrate, and applying a voltage to the electrode, thereby creating a potential differential between the first substrate and the second substrate that generates an electrostatic force between the first and second substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/173,489, filed Feb. 5, 2014, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present technology is related to semiconductor devices, systems andmethods. In particular, some embodiments of the present technology arerelated to devices, systems and methods for enhanced bonding betweensemiconductor materials.

BACKGROUND

In semiconductor manufacturing, several processes exist for adding alayer of material to a semiconductor substrate, including transferring alayer of material from one semiconductor substrate to another. Suchprocesses include methods for forming silicon-on-insulator (“SOI”)wafers, semiconductor-metal-on-insulator (“SMOI”) wafers, andsilicon-on-polycrystalline-aluminum-nitride (“SOPAN”) wafers. Forexample, FIGS. 1A-1D are partially schematic cross-sectional viewsillustrating a semiconductor assembly in a prior art method fortransferring a silicon material from one substrate to another. FIG. 1Aillustrates a first substrate 100 including a base material 104 and anoxide material 102 on the base material 104. As shown in FIG. 1B, asecond substrate 120 is then positioned on the first substrate 100 forbonding (as indicated by arrow A). The second substrate 120 alsoincludes a silicon material 124 and an oxide material 122 on the siliconmaterial 124. The second substrate 120 is positioned on the firstsubstrate 100 such that the first substrate oxide material 102 contactsthe second substrate oxide material 122 and forms an oxide-oxide bond.The silicon material 124 has a first portion 124 a and a second portion124 b delineated by an exfoliation material 130 at a selected distancebelow a downwardly facing surface of the first portion 124 a. Theexfoliation material 130 can be, for example, an implanted region ofhydrogen, boron, and/or other exfoliation agents.

FIG. 1C illustrates the semiconductor assembly formed by bonding thefirst substrate 100 to the second substrate 120. Once the substrates100, 120 are bonded, the first portion 124 a of the semiconductormaterial 124 is removed from the second portion 124 b by heating theassembly such that the exfoliation material 130 cleaves the siliconmaterial 124. The second portion 124 b remains attached to the firstsubstrate 100, as shown in FIG. 1D, and has a desired thickness forforming semiconductor components in and/or on the second portion 124 b.The first portion 124 a of the silicon material 124 can be recycled tosupply additional thicknesses of silicon material to other firstsubstrates.

One challenge of transferring silicon materials from one substrate toanother is that poor bonding between the first and second substrates cangreatly affect the yield and cost of the process. In transfer processes,“bonding” generally includes adhering two mirror-polished semiconductorsubstrates to each other without the application of any macroscopicadhesive layer or external force. During and/or after the layer transferprocess, poor bonding can cause voids, islands or other defects betweenthe two bonded substrate surfaces. For example, the material propertiesof certain materials can result in poor bonding, such as silicon with ametal of SMOI or a poly-aluminum nitride surface with silicon of SOPAN.

Conventional bonding processes also include applying an externalmechanical force (e.g., a weight or a compressive force) to the firstand second substrates for a period of time. In addition to adding time,adding cost, and reducing throughput, bonding processes that use anexternal force suffer from several drawbacks. First, the downward forceapplied on the second substrate is not distributed uniformly and cancause defects in the substrate or even break one or both substrates.Second, because the force is not distributed uniformly, the magnitude ofthe applied mechanical force is limited to the maximum allowed force inthe area with the highest force concentration, which means that otherareas of the substrate do not experience the maximum force. Third, theuse of an external mechanical force can contaminate the semiconductorassembly. Last, some semiconductor devices can have large depressions inthe under-layer topography because of dishing from priorchemical-mechanical planarization processing making it difficult to bondthe oxide layers to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present technology can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale. Instead, emphasis is placed on illustratingclearly the principles of the present technology.

FIGS. 1A-1D are schematic cross-sectional views of various stages in amethod for transferring and bonding a semiconductor layer according tothe prior art.

FIG. 2A is a schematic cross-sectional view of a bonding systemconfigured in accordance with the present technology.

FIG. 2B is a schematic cross-sectional view of the bonding system inFIG. 2A supporting a semiconductor assembly.

FIG. 3 is a schematic cross-sectional view of a bonding systemconfigured in accordance with another embodiment of the presenttechnology.

DETAILED DESCRIPTION

Several embodiments of the present technology are described below withreference to processes for enhanced substrate-to-substrate bonding. Manydetails of certain embodiments are described below with reference tosemiconductor devices and substrates. The term “semiconductor device,”“semiconductor substrate,” or “substrate” is used throughout to includea variety of articles of manufacture, including, for example,semiconductor wafers or substrates of other materials that have a formfactor suitable for semiconductor manufacturing processes. Several ofthe processes described below may be used to improve bonding on and/orbetween substrates.

FIGS. 2A-3 are partially schematic cross-sectional views of enhancedbonding systems and methods in accordance with embodiments of thetechnology. In the following description, common acts and structures areidentified by the same reference numbers. Although the processingoperations and associated structures illustrated in FIGS. 2A-3 aredirected to SOI-based transfers, in certain embodiments the process canbe used to enhance bonding in other material-based transfer layermethods, such as SMOI-based transfers, SOPAN-based transfers, and thelike.

FIG. 2A is a cross-sectional side view of one embodiment of an isolatedbonding system 300 (“system 300”), and FIG. 2B is a cross-sectional sideview of the system 300 supporting a substrate assembly 307. As shown inFIG. 2B, the substrate assembly 307 includes a first substrate 303(e.g., a handling substrate) and a second substrate 305 (e.g., a donorsubstrate) on the handling substrate 303. The first substrate 303 canhave a base material 306 and first oxide layer 308, and the secondsubstrate 305 can include a semiconductor material 310 and a secondoxide layer 309. The base material 306 can be an insulator, polysiliconaluminum nitride, a semiconductor material (e.g., silicon (1,0,0),silicon carbide, etc.), a metal, or another suitable material. Thesemiconductor material 310 can include, for example, a silicon wafermade from silicon (1,1,1) or other semiconductor materials that areparticularly well suited for epitaxial formation of semiconductorcomponents or other types of components. In other embodiments, only oneof the first or second substrates 303, 305 may include an oxide layer.Additionally, the orientation of the first and second substrates 303 and305 can be inverted relative to the orientation shown in FIG. 2B.

As shown in FIG. 2B, the second substrate 305 can be positioned on thefirst substrate 303 such that the second oxide layer 309 of the secondsubstrate 305 contacts the first oxide layer 308 of the first substrate303. As such, the shared contact surfaces of the first and second oxidelayers 308, 309 form a bonding interface 322 between the first andsecond substrates 303, 305. Additionally, the first and second oxidelayers 308, 309 form a dielectric barrier 320 between the first andsecond substrates 303, 305. The dielectric barrier 320 can have athickness d that is between about 1 nm and about 20 μm. In a particularembodiment, the dielectric barrier 320 can have a thickness d that isbetween about 1 μm and about 10 μm.

Referring to FIGS. 2A and 2B together, the system 300 can include aunipolar electrostatic chuck (ESC) 301 having an electrode 304, aconductor 312, and a power supply 314. In some embodiments, the ESC 301includes a dielectric base 302 that carries the electrode 304. Theelectrode 304 can include a support surface 316 configured to receivethe first substrate 303 and/or the substrate assembly 307. The powersupply 314 is coupled to the electrode 304 and configured to supply avoltage to the electrode 304, and the conductor 312 is electricallycoupled to a ground source G. The substrate assembly 307 can bepositioned on the support surface 316 of the electrode 304, and theconductor 312 can contact a portion of the substrate assembly 307opposite the dielectric barrier 320. In the embodiment shown in FIG. 2Bthe first substrate 303 contacts the electrode 304 and the secondsubstrate 305 contacts the conductor 312.

The conductor 312 can be a single contact pin or pad connected to theground source G via a connector 318. The conductor 312 can be configuredto engage all or a portion of the surface of the substrate assembly 307facing away from the ESC 301. For example, as shown in FIG. 2B, theconductor 312 can be a pad that covers only a portion of the surface ofthe second substrate 305, and the conductor 312 can be positioned at thecenter of the second substrate 305. In other embodiments, the conductor312 can contact any other portion of the second substrate 305 and/or theconductor 312 can have the same size as the second substrate (shown indashed lines). Although the conductor 312 includes only a single contactpad in the embodiment shown in FIG. 2B, in other embodiments theconductor 312 can have multiple pins, pads or other conductive featuresconfigured in a pattern to provide the desired current distributionacross the second substrate 305. In other embodiments, the conductor 312can have any size, shape and/or configuration, such as concentric rings,an array of polygonal pads, etc.

Unlike conventional ESCs, the ESC 301 of the present technology does nothave a dielectric layer separating the electrode 304 from the firstsubstrate 303 and/or substrate assembly 307. In other words, when thefirst substrate 303 is on the support surface 316, the first substrate303 directly contacts the electrode 304 without a dielectric materialattached to the support surface 316 of the electrode 304. Although insome cases a bottom surface of the first substrate 303 may include anative oxide film, the film is very thin (e.g., 10-20 Å) and thusprovides negligible electrical resistance between the electrode 304 andthe first substrate 303. As a result, voltages applied to the electrode304 pass directly to the first substrate 303. Because the firstsubstrate 303 directly contacts the electrode 304 and has negligibleinternal resistance, a conventional bi-polar or multi-polar ESC cannotbe used with the system 300 as the first substrate would provide adirect electrical connection between the electrodes and short thesystem.

In operation, the first substrate 303 is positioned on the supportsurface 316 in direct electrical contact with the electrode 304. If thesecond substrate 305 is not already positioned on the first substrate303, the second substrate 305 can be manually or robotically placed onthe first substrate 303. For example, as shown in FIG. 2B, the connector318 can be in the form of a conductive robotic arm that can support thesecond substrate 305 and move the second substrate 305 over the firstsubstrate 303. The robotic arm can include a negative pressure source(not shown) at one end that engages and holds the second substrate 305until a desired position is achieved.

Once the second substrate 305 is in position for bonding with the firstsubstrate 303, the conductor 312 can be placed in contact with thesecond substrate 305. The power supply 314 is then activated to apply avoltage to the electrode 304. As previously discussed, the firstsubstrate 303 operates as a continuation of the electrode 304 becausethe first substrate 303 directly contacts the electrode 304 without adielectric material between the two. As a result, an electrical chargeaccumulates at or near a top surface 303 a of the first substrate 303thereby causing an opposite electrical charge to accumulate at or near abottom surface 305 a of the second substrate 305. Accordingly, anelectric potential is established across the dielectric barrier 320between the first and second substrates 303, 305. The electric potentialcreates an electrostatic force F that pulls the second substrate 305towards the first substrate 303 and enhances the bond between the firstand second substrates 303, 305.

The electrostatic force F generated by the system 300 is significantlygreater than that of conventional systems because it improves theelectrical contact with the first substrate and decreases the dielectricdistance between the first and second substrates 303, 305. The magnitudeof the electrostatic force F can be determined by the following equation(1):

$\begin{matrix}{{F = {\frac{1}{2}{ɛ_{0}\left( \frac{kV}{d} \right)}^{2}}},} & (1)\end{matrix}$

where

k is a dielectric constant;

d is the dielectric thickness; and

V is the applied voltage.

As indicated by the equation (1), the smaller the dielectric thickness dand/or the greater the applied voltage V, the greater the electrostaticforce F. As such, the magnitude of the electrostatic force F can becontrolled by adjusting the applied voltage V and/or the dielectricthickness d. In some embodiments, the system 300 can include acontroller (not shown) that automatically controls the magnitude,duration, and/or timing of the electrostatic force F by adjusting theapplied voltage V.

The system 300 and associated methods are expected to provide severaladvantages over conventional methods for enhanced substrate bonding thatapply an external mechanical force. First, the magnitude of theelectrostatic force F achieved by the system 300 is considerably greaterthan the compressive force imposed by conventional mechanical forceapplications. By way of example, on a 6-inch wafer, mechanicalforce-generating devices can apply a maximum force of 100 kN, while thecurrent system can generate an electrostatic force F of greater than 200kN. Also, in contrast to conventional methods and systems, the system300 can evenly distribute the electrostatic force F across thesubstrates 303, 305. As evidenced by equation (1) above, the magnitudeof the electrostatic force F is only dependent on two variables: theapplied voltage V and the dielectric thickness d. Both the appliedvoltage V and the dielectric thickness d are intrinsically constantacross the cross-sectional area of the substrates 303, 305.Additionally, in conventional methods utilizing a mechanical compressiveforce, the handling substrate and/or substrate assembly would have to bemoved from one machine to the next and/or a force-generating machinewould have to be moved into the vicinity of the handling substrateand/or substrate assembly. The current system, however, does not requireany moving of machine or substrates and can achieve enhanced bonding byadjusting the applied voltage. As such, the system 300 of the presenttechnology can be operated at a lower cost and higher throughput.

FIG. 3 is a cross-sectional side view of another embodiment of a bondingsystem 400 (“system 400”) configured in accordance with the presenttechnology. The first substrate 403, second substrate 405 and ESC 401can be generally similar to the first substrate 303, second substrate305 and ESC 301 described in FIGS. 2A and 2B, and like referencenumerals refer to the components. However, instead of having a conductorin the form of a conductive pin or pad as shown in FIG. 3, the system400 includes a plasma source 424, a plasma chamber 422 filled with aplasma gas P that defines a conductor 423 electrically coupled to theplasma gas P. The plasma gas P is electrically conductive such that theplasma gas P is also a conductor. The conductor 423, for example, can beelectrically connected to a ground source G via an electrical element412 (e.g., an antenna, an electrode, etc.). As shown in FIG. 3, theplasma chamber 422 extends around at least a portion of the secondsubstrate 405. As such, the first substrate 403 and/or the electrode 404is electrically isolated from the plasma chamber 422.

The plasma gas P can be a noble, easily ionized plasma gas, such asArgon (Ar), Helium (He), Nitrogen (N₂), and others. The plasma source424 can be an inductively coupled-plasma (“ICP”) source, microwave,radiofrequency (“RF”) source and/or other suitable sources. A plasma gasin bulk acts as a virtual conductor. As the plasma gas P is releasedinto the plasma chamber 422, the plasma gas P charges the secondsubstrate 405. Activation of the power supply 414 creates a potentialdifference across the dielectric barrier 420, thereby generating anelectrostatic force F between the substrates 403, 405.

In some embodiments, the system 400 can also include a vacuum source 426connected to the plasma chamber 422 that draws the plasma gasdownwardly. The system 400 can also include additional featurestypically associated with vacuum chamber systems, such as powerconditioners (e.g., rectifiers, filters, etc.), pressure sensors, and/orother suitable mechanical/electrical components.

The system 400 provides several advantages over conventional systems,including those advantages discussed above with reference to the system300. Additionally, the system 400 can reduce contamination as theenhanced bonding is carried out in a pressurized, sealed plasma chamber422.

Any of the above-described systems and methods can include additionalfeatures to expedite substrate processing. For example, any of the abovesystems can include one or more features to automate the bonding and/orlayer transfer process, such as lift pins and/or robotic transfer armsfor loading and unloading the substrates from the system.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thescope of the invention. Accordingly, the invention is not limited exceptas by the appended claims.

I/We claim:
 1. A method for enhancing wafer bonding, the methodincluding: positioning a substrate assembly on a unipolar electrostaticchuck (“ESC”), the ESC having an electrode; positioning a firstsubstrate of the substrate assembly on the electrode, wherein thesubstrate assembly further includes a second substrate on the firstsubstrate; electrically coupling a conductor to the second substrate;applying a voltage to the electrode, thereby creating an electricalpotential between the first substrate and the second substrate.
 2. Themethod of claim 1 further comprising applying the voltage from a powersupply to the electrode.
 3. The method of claim 1 further comprisingaccumulating a first electrical charge at or near a bottom surface ofthe second substrate by accumulating a second electrical charge at ornear a top surface of the first substrate, wherein the first electricalcharge and the second electrical charge are opposite.
 4. The method ofclaim 1 further comprising urging the second substrate towards the firstsubstrate at a force of at least 200 kN.
 5. The method of claim 1further comprising adjusting an electrostatic force between the firstand second substrates by adjusting the voltage applied to the firstelectrode.
 6. The method of claim 5 further comprising uniformlydistributing the electrostatic force across a top surface of the firstsubstrate and a bottom surface of the second substrate.
 7. The method ofclaim 1 wherein the conductor comprises a contact pad, and electricallycoupling the second substrate to the conductor includes positioning thecontact pad in direct contact with the second substrate.
 8. The methodof claim 1 wherein the conductor comprises a plasma gas, andelectrically coupling the second substrate to the conductor includeselectrically biasing the plasma gas while the plasma gas contacts thesecond substrate.
 9. The method of claim 1 further comprising sealingthe substrate assembly in a pressurized chamber while urging the secondsubstrate against the first substrate.
 10. A system for enhancingbonding between a first substrate and a second substrate, the systemcomprising: a unipolar electrostatic chuck configured to receive thefirst substrate, the chuck including a dielectric base and an electrodeat least partially within the dielectric base, wherein a top surface ofthe electrode is configured to directly electrically contact the firstsubstrate; a conductor configured to be electrically coupled to thesecond substrate; and a power supply electrically coupled to theelectrode and conductor, respectively, to apply an electrical biasbetween the electrode and conductor.
 11. The system of claim 10 whereinthe unipolar electrostatic chuck does not include a dielectric layerbetween the electrode and the first substrate.
 12. The system of claim10 wherein the conductor includes a contact pad.
 13. The system of claim12 wherein the contact pad is configured to contact at least a portionof a top surface of the second substrate.
 14. The system of claim 10,further comprising an electrical element positioned in a plasma chamberconfigured to energize a plasma gas in the plasma chamber.
 15. Thesystem of claim 14 wherein the plasma chamber is configured to contactat least a portion of the second substrate and is electrically isolatedfrom the first substrate.
 16. The system of claim 14, further comprisinga vacuum source coupled to the plasma chamber.
 17. A method forenhancing wafer bonding utilizing a unipolar electrostatic chuck, theelectrostatic chuck including an electrode, the method including:electrically coupling the electrode to a first substrate; electricallycoupling a conductor to a second substrate positioned on the firstsubstrate, wherein the first substrate and the second substrate areseparated by a dielectric barrier; and exerting opposing forces on thetop and bottom surfaces of the dielectric barrier.
 18. The method ofclaim 17, further comprising electrically isolating the first substratefrom the second substrate.
 19. The method of claim 17, furthercomprising applying a voltage from a power supply to the first substratevia the electrode.
 20. The method of claim 17, further comprisingaccumulating a first electrical charge at or near a bottom surface ofthe second substrate by accumulating a second electrical charge at ornear a top surface of the first substrate, wherein the first electricalcharge and the second electrical charge are opposite.